And when you request 1900 as a note on your reservation, add the length of your trailer so that they will see that and, along with assuming for your tow vehicle, try to assign you to a site that will accommodate your length on the first go-around.
A computer system pre-assigns campsite numbers based on what will available on the day you arrive but Fort personnel can and do make changes to those pre-assignments a few days before arrival. So if you can pass that info to them via the system, they are good about catching it and trying to do something about it.
Bama Ed
PS - all the site levels have full (as in "all") hookups except the Tent/Pop-up level (has no sewer hook). Full and Preferred levels are the same except for their location inside the Fort (Preferred down by the lake, Full back in the quiet corner) with a gravel tent/back pad. Premium and Premium Meadow levels are the same (wider/longer all paved no gravel) except for their location inside the Fort (Premium Meadow named for being close to the Meadow area which has pool, trading post, bike barn, campfire/movie singalong).